In recent years, attention has been given to display devices in which a touch detection device referred to as a so-called touch panel is provided on a display device such as a liquid crystal display device, or a touch panel and a display device are integrated as a single body, and the display device is made to display various button images to enable information to be input without ordinary real buttons. Such display devices having a touch detection function do not need input devices such as a keyboard, a mouse and a keypad, and thus tend to be broadly used as display devices of computers, portable information terminals such as cell phones, etc.
As such a touch panel, a capacitive touch panel is known in which a plurality of electrodes each formed to extend in a single direction are intersected to each other. In this touch panel, the electrodes are connected to a control circuit, and when supplied with an excitation current from the control circuit, they detect an object close thereto.
As a display device provided with a touch sensor, a so-called in-cell touch panel is proposed in addition to a so-called on-cell touch panel in which a touch panel is provided on a display surface of a display device. In the in-cell display device, a common electrode for display, which is originally provided in the display device, is also used as one of a pair of electrodes for a touch sensor, and the other of the pair of electrodes (a touch detection electrode) is provided to intersect the common electrode.
Furthermore, as methods of detecting a touch position, a mutual detection method and a self-detection method are known. In the mutual detection method, a drive signal of alternating voltage is input to one of electrodes, and a detection signal generated in the other electrode by the drive signal is processed, to thereby detect a touch position. In the self-detection method, drive signals of alternating voltage are input to electrodes, respectively, and signals generated in the electrodes, respectively, are processed, to thereby detect a touch position.
On the other hand, a technique of performing detection with a high sensitivity has been applied. In this technique, a stylus pen referred to as an active pen which generates static electricity is detected or a finger or the like which is in a floating state in which the finger or the like does not touch a touch panel is detected. In such a manner, in order to detect an object with a high sensitivity, the self-detection method, not the mutual detection method, is more frequently applied.